ECG Quiz Answer – First degree AV block, sinus pause, QT prolongation
First degree AV block, sinus pause, QT prolongation: PR interval is prolonged and measures 240 ms. A sinus pause of 1880 ms is seen at the end of the tracing. Together these indicate dual nodal (atrioventricular and sinoatrial node) dysfunction. An interesting finding is the recovery of AV conduction after the long pause so that PR interval in the beat following the pause is only 120 ms.
QT interval is 440 ms with a cycle length of 640 ms, indicating a QTc of around 550 ms. It may be noted that the QT prolongation is predominantly due to prolongation of ST segment. ST prolongation contributing to QT prolongation is characteristic of hypocalcemia. This is because calcium is the ion predominantly involved in the phase 2 (plateau phase) of the myocardial action potential.